1. Field of the Invention
The present invention relates to a drawing apparatus which performs drawing on a substrate with a plurality of charged particle beams, and a method of manufacturing an article.
2. Description of the Related Art
In recent years, with an increase in packing density and miniaturization of semiconductor integrated circuits, the line width of a pattern formed on a substrate has become very small. To keep up with this trend, a finer pattern must be transferred in a lithography process in which a resist pattern is formed on a substrate. A drawing scheme that uses an electron beam is known as one method which meets such a requirement for pattern miniaturization. An electron beam drawing apparatus converges an electron beam emitted by an electron gun on a desired position on a substrate via an electron optical system, and relatively moves the electron beam and a stage which mounts the substrate, thereby drawing a pattern on the substrate. Hence, to form a fine pattern, it is of prime importance to accurately align the relative position between the electron beam and the substrate with as much as possible.
One factor which degrades the alignment accuracy between the electron beam and the substrate is a drift of the electron beam resulting from charge-up or heat. In electron beam drawing, charge-up of the electron optical system occurs due to electron scattering, and that of the substrate occurs upon electron beam irradiation. Also, deformation of the electron optical system and substrate occurs due to the influence of heat produced upon electron beam irradiation in drawing. When this occurs, a drift of the electron beam is generated upon a shift in irradiation position of the electron beam guided from the electron optical system onto the substrate or a change in electron beam trajectory due to factors associated with a charge distribution on the substrate. This poses a problem that the alignment accuracy in electron beam drawing degrades, thus deteriorating the pattern processing accuracy.
To solve the problem resulting from a drift of the electron beam due to charge-up, the following techniques have been proposed. Japanese Patent Laid-Open No. 2001-168013 describes an electron beam drawing method of using an electron detector which detects secondary electrons from the substrate to measure the position of each alignment mark formed on the substrate, thereby correcting a drift of the electron beam. In the method described in Japanese Patent Laid-Open No. 2001-168013, the alignment mark is irradiated with the electron beam at a predetermined timing after the start of drawing, and secondary electrons from the substrate are detected by the electron detector, thereby measuring the position of the alignment mark. Then, in the method described in Japanese Patent Laid-Open No. 2001-168013, the amount of drift of the electron beam is calculated based on the difference from the previous measurement result, and the calculation result is superposed on the amount of deflection of the electron beam, thereby correcting a drift of the electron beam.
Japanese Patent Laid-Open No. 2000-049069 describes an electron beam drawing apparatus which corrects a drift of the electron beam based on the position measurement result of each alignment mark obtained using the electron beam, and that obtained using light. The electron beam drawing apparatus described in Japanese Patent Laid-Open No. 2000-049069 includes an electron detector which detects secondary electrons from the substrate upon scanning the alignment mark using the electron beam, and an alignment optical system which irradiates the alignment mark with light and receives the light reflected by it. The electron beam drawing apparatus then calculates the amount of drift of the electron beam based on the position of the alignment mark measured using the light only once before the start of drawing, and that measured using the electron beam after the start of drawing. The electron beam drawing apparatus then corrects the position, to which the electron beam is deflected or the stage position, based on the calculated amount of drift, thereby correcting the drawing position of the electron beam.
Japanese Patent Laid-Open No. 63-263720 describes an electron beam drawing apparatus which corrects a positional shift between the electron beam and the substrate based on the position measurement result of each mark obtained using a mark measurement electron beam. The electron beam drawing apparatus described in Japanese Patent Laid-Open No. 63-263720 includes a mark measurement electron optical system, separately from a drawing electron optical system. The electron beam drawing apparatus sets the acceleration voltage of a mark measurement electron beam, emitted by a mark measurement electron gun, to a condition optimum for mark detection in accordance with the material and shape of the mark, and performs pattern drawing and mark measurement in parallel. The electron beam drawing apparatus then aligns the electron beam and the substrate based on the measurement result to correct the drawing position of the electron beam.
However, when the drawing operation is interrupted, and mark position measurement is performed upon driving the stage to move the alignment mark to the measurement position, the stage driving time and the mark position measurement time are necessary, separately from the drawing time, thus lowering the throughput. Therefore, it is difficult to achieve a high throughput using an electron beam drawing apparatus which performs mark position measurement upon interrupting the drawing operation after the start of drawing, as in Japanese Patent Laid-Open Nos. 2001-168013 and 2000-049069.
On the other hand, since the electron beam drawing apparatus as described in Japanese Patent Laid-Open No. 63-263720 can perform drawing and mark measurement in parallel, it can avoid degradation in throughput upon interrupting the drawing operation. However, both electron guns and electron optical systems are separately provided for drawing and mark measurement, so the amount of drift of the electron beam is not always equal in the two electron optical systems. Therefore, even when a shift in drawing position of the electron beam is corrected based on the measurement result using the mark measurement electron optical system, it is impossible to accurately correct a drift in the drawing electron optical system. Furthermore, providing two sets of an electron gun and an electron optical system for drawing and mark measurement leads to an increase in size, complication, and a rise in cost of the drawing apparatus.